1. Field of the Invention
The present invention relates to an image processing apparatus which embeds additional information in image data, and an image forming apparatus which is equipped with the image processing apparatus and forms an image according to the image data in which the additional information is embedded.
2. Related Art
Recently, in view of document management or security protection, image processing apparatuses that are capable of embedding predetermined information in an image as watermark information (such information is hereafter referred to as “additional information” as it is added to image data) have been developed. Such an image processing apparatus embeds additional information into an image when the image is outputted onto a recording sheet such as plain paper (a recording sheet onto which an image has been outputted is hereafter referred to as a “hard copy”).
For example, U.S. Pat. No. 5,987,127 discloses the following copying machine. When a hard copy embedded with additional information is copied as an original, (a copy made from a hard copy is hereinafter referred to as a “secondary copy”), the copying machine extracts the additional information embedded in image data read from the original by a scanner, and analyzes the additional information to perform predetermined copy management. The copying machine updates the extracted additional information such as a copy creation date and embeds the updated additional information in the secondary copy.
As described above, when the hard copy embedded with additional information, such as a copy creation date which needs to be updated every time the image is outputted, is copied as an original, the additional information is updated and embedded in the secondary copy. This is particularly meaningful in such a case where the original is an important literary work, for which conditions such as a copy expiry date have been set, because the document management can be performed strictly by reading out the date information embedded in the secondary copy and using the read date information for judging whether another copy of the hard copy is allowed to be made.
However, when image processing apparatuses (for example, copying machines) of different manufacturers are used, or when image processing apparatuses of the same manufacturer are used but formats for embedding additional information into an image are different depending on their models, an image processing apparatus may not be able to analyze the read additional information embedded by another image processing apparatus. In such a case, additional information, such as the above mentioned date information, that needs to be updated, cannot be updated, which could undermine accurate document management thereafter. Also, even if the additional information cannot be analyzed by one image processing apparatus, there is a possibility that another image processing apparatus (for instance, an image processing apparatus of the same model as an image processing apparatus that has embedded the additional information) can analyze the additional information. Therefore, it is preferable to retain the additional information in a state where it can be utilized later.